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to prevailing outdoor temperature
and defines zones of 80% and 90%
satisfaction.
The tool’s operative minimum
and maximum comfort temperature
benchmarks automatically adjust
according to the input data, which
ranged between approximately 15 ºC
and 32 ºC. The operative temperature
can be defined as the average of the
mean radiant and ambient tempera-
tures weighted by their respective
heat transfer coefficients.
The personal factors and humid-
ity are not significant in this method
since adaptation is considered, and
the only variable is the outdoor
temperature. The mean radiant tem-
perature of the enclosing surface of a
space is determined by the emissiv-
ity and temperature of the surfaces.
According to Holm and Engelbrecht
small floor areas and low ceilings
force radiant temperature to be clos-
er to the dry-bulb air temperature
and therefore for this investigation
taken as the same value.
The input data for the thermal
comfort tool was the real-time data
collected from the loggers for the
indoor and outdoor temperatures for
each house to individually establish
whether the temperatures fell within
the relevant ASHRAE 55 comfort
ranges (benchmarks) for the relevant
winter and summer periods.
Due to the variables for each
house being different, direct com-
parisons are not made in this phase
of the research. The mean radiant
temperature for the first exercise
is taken as the indoor dry-bulb air
temperature.
Conclusion
For this investigation, focus was
on the thermal performance of IBT
houses and whether they complied
with the ASHRAE 55 Adaptive model
thermal comfort ranges.
The poor winter results revealed
that more research is required on
design of IBT houses for thermal
performance in different climate
zones. Considering these houses
were built before 2011, when the
SANS 10400XA standard on energy
efficiency requirements came into
operation, there is now a better
benchmark according to which IBT
houses can be designed for ensuring
thermal comfort.
The question on whether the
relevant IBT houses comply with
comfort ranges has been addressed,
but still need to uncover the rea-
sons for the relevant performance.
Through the use of a certified energy
efficiency software one will be able
to complete the modelling of the at
least one IBT house falling within the
relevant different categories (light
weight to heavy weight) to establish
the variables that contributed to the
performance.
The variables that could have had
an influence on the thermal comfort
can range from issues related to
orientation, window position and
sizes, thermal mass, insulation, cross
ventilation and shading. One can
then also ascertain whether radiant
temperature would have made a
significant difference in the results.
The thermal ratings will be avail-
able on the newdynamic newNHBRC
IBT Database.
■
‘as-built’ IBT houses
the windows were closed during the
data collection process. However,
this approach does not reflect the
real temperatures in the case of an
occupied housewhere openwindows
allow for cross ventilation. Cross ven-
tilation could possibly improve the
indoor comfort, but cannot be plau-
sibly determined in this phase of the
analysis. Reasons why the relevant
IBT houses were not thermally com-
fortable were also not established for
this investigation.
Methodology and Analysis
For the sampling, calibrated Keytag
KTL – 508 Temperature and Humidity
data loggers were used, which came
with a certificate of compliance. For
this phase, two instruments (north
and south) were set up per house
in peak winter and summer periods
for one month. Being part of the first
stage of the project some interest-
ing deductions were made on this
analysis in terms of thermal comfort
considering indoor and outdoor
temperatures for naturally ventilated
buildings according the ASHRAE 55
(2013) Adaptive method.
The data was analysed using the
web-based tool for thermal comfort
calculations according to ASHRAE
Standard 55 (2013), developed by
the University of California at Berk-
ley. The main features of the Adap-
tive method, applicable to naturally
ventilated buildings, included input
variables such as dry-bulb air tem-
perature, mean radiant temperature
and prevailing mean outdoor tem-
perature. The adaptive chart/tool re-
lates to indoor comfort temperature